title: Crystal structure of importin-α bound to a peptide bearing the nuclear localisation signal from chloride intracellular channel protein 4.
abstract: It has been reported that a human chloride intracellular channel (CLIC) protein, CLIC4, translocates to the nucleus in response to cellular stress, facilitated by a putative CLIC4 nuclear localization signal (NLS). The CLIC4 NLS adopts an α-helical structure in the native CLIC4 fold. It is proposed that CLIC4 is transported to the nucleus via the classical nuclear import pathway after binding the import receptor, importin-α. In this study, we have determined the X-ray crystal structure of a truncated form of importin-α lacking the importin-β binding domain, bound to a CLIC4 NLS peptide. The NLS peptide binds to the major binding site in an extended conformation similar to that observed for the classical simian virus 40 large T-antigen NLS. A Tyr residue within the CLIC4 NLS makes surprisingly favourable interactions by forming side-chain hydrogen bonds to the importin-α backbone. This structural evidence supports the hypothesis that CLIC4 translocation to the nucleus is governed by the importin-α nuclear import pathway, provided that CLIC4 can undergo a conformational rearrangement that exposes the NLS in an extended conformation.
authors.affiliation: School of Physics, University of New South Wales, Sydney, NSW, Australia.
authors.forename: Andrew V
authors.initials: AV
authors.lastname: Mynott
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Harrop
authors.forename: Louise J
authors.initials: LJ
authors.lastname: Brown
authors.forename: Samuel N
authors.initials: SN
authors.lastname: Breit
authors.forename: Bostjan
authors.initials: B
authors.lastname: Kobe
authors.forename: Paul M G
authors.initials: PM
authors.lastname: Curmi
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D000957:Antigens, Viral, Tumor / Q000378:metabolism; D001665:Binding Sites; D018118:Chloride Channels / Q000378:metabolism*; D018360:Crystallography, X-Ray; D006801:Humans; D051379:Mice; D019913:Nuclear Localization Signals / Q000378:metabolism; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D028901:alpha Karyopherins / Q000378:metabolism*
chemical_list: D000957:Antigens, Viral, Tumor; C464459:CLIC4 protein, human; D018118:Chloride Channels; D019913:Nuclear Localization Signals; D028901:alpha Karyopherins